The present invention relates to safety valves for controlling excessive flow rates through a delivery system; the invention particularly relates to an air valve for controlling the volumetric flow rate of air through pressurized lines, wherein a feature is provided for testing the operation of the valve under normal flow conditions.
Runaway control valves are known in the art, where they are typically used to shut down a pressurized air line whenever flow rate exceeds predetermined values. Such valves typically utilize a pressure-sensitive valve member which monitors pressure drop across a portion of the pressure line, and when the pressure drop exceeds a predetermined amount the movable valve member closes off the line. Once the pressure line has been closed in this manner, most prior art valves require that the valve be manually reset in order to reopen the line for pressurized gas flow.
One example of an application for a runaway control valve is in an air-operated motor and pumping system, particularly of the type where the pressurized air supply is used to energize a reciprocable air motor, and the air motor is mechanically linked to a liquid pump. In this type of system, the reciprocation rate of the air motor is a function of the air pressure applied to its input as balanced against the liquid pressure forces of the pumped output. If the pump liquid is caused to flow freely, as by opening some sort of liquid delivery valve, the loading of the air motor decreases and the air supply into the air motor causes it to reciprocate at a faster rate; this causes the pump to reciprocate at a faster rate and increases the volume of liquid delivered through the line. At some point a balance is reached whereby the liquid delivered by the pump is equal to the liquid drained from the system and the pressure is equalized. At this point the air motor reciprocates at a regular rate, sufficient to continue the flow of liquid. If, for example, the liquid delivery line ruptures and causes an uncontrolled drain of liquid, the air motor will reciprocate at an ever increasing rate to attempt to equalize the delivery flow rates, which may become impossible because of the nature of the rupture. In such situations, a runaway flow control valve inserted into the pressurized air line which drives the air motor is essential, for the runaway valve detects the excessively high flow rates of air delivered to the motor and automatically shuts off the air source to the air motor. Without a runaway flow control valve in such a system, the air motor could reciprocate at an increasing rate until self destruction occurs.
Among the disadvantages of prior art runaway valves is that it is difficult to test the valve in order to ascertain whether it is in proper operating condition, without actually creating the runaway flow conditions which can trigger the valve. Therefore, the operability of such valves only becomes known as a result of an actual system failure which creates the runaway flow conditions; however, if the valve fails under these actual conditions a catastrophic result could occur. It therefore would be an advantage if a safety test feature could be provided for such valves, in order to evaluate operability of the valve under other than catastrophic conditions.